1. Field of the Invention
This invention relates to various hawser configurations which can be used on a semi-submersible tender adapted for facilitating servicing off shore oil and natural gas production platforms, subsea wells, and other subsea infrastructure in water depths up to 10,000 feet.
The present invention specifically relates to a semi-submersible tender which can be secured to different types of production platforms, such as a tension leg platform (TLP), a deep draft caisson vessel (SPAR), a fixed platform, a compliant tower, a semi-submersible production vessel, or a floating vessel.
2. Background of the Invention
It is very expensive to provide a production platform with adequate space for all the drilling and completion equipment needed to safely drill and complete a well, as well as store drilling and completion equipment and materials in an environmentally conscientious manner, including drilling and completion risers, casings, tubings and drilling and completion fluids. Tenders have often been called into service to provide the required space needed on a rig and/or platform during the initial drilling and completion phase of an oil lease. Problems have traditionally existed in that most tenders cannot be kept alongside a platform in a constant spaced relationship during extreme weather without colliding with the platform. Specifically, tenders have not been able to remain in a connected capacity and avoid the risk of collision. Most commercial tenders cannot provide a high operational weather window to the tender and rig, and still endure the environmental load of up to a 10-year storm. See U.S. Pat. Nos. 4,065,934, and 4,156,577, which are hereby incorporated by reference on currently known tenders for production platforms. Most tenders have to be completely towed away to a safe location in the case of a tropical storm or extreme weather, which causes considerable expense to the drilling contractor and/or customer.
A need has long existed for systems that can synchronize a tender with platforms in water depths exceeding several hundred feet for long periods of time and in the presence of serious storms.
The present invention relates to various hawser connection configurations used in combination with a unique semisubmersible tender which not only can provide up to 25,000 square feet of additional deck space but also over 8000 barrels of liquid storage capacity. These unique hawser configurations enable the tender to keep a constant distance from a production platform while synchronizing the tender""s low and mean movement frequencies with the platform, which enables the tender to follow the mooring watch pattern of the production platform, such as a figure eight pattern, or elliptical pattern, and sustain without damage, the environmental load of wind, current and wave forces of a 100-year cyclonic storm (such as a hurricane) in the 100-year extreme weather standby position, and up to a 10-year storm in a tendering position.
The invention is related to hawser use and design, which have significant environmental and safety advantages over known systems and known tenders.
The invention relates to the use of hawser in association with a semisubmersible tender which utilizes pre-set anchors and can be tendered to a production platform for assisting in the drilling and completion and recovery of oil and gas in weather that can be up to a 10-year storm and maintaining a standby position in weather up to a 100-year hurricane.
The invention relates to a hawser system for connecting a semisubmersible tender to a deep draft caisson vessel comprising: a first winch and a second winch disposed on the first end of the tender; a first hawser connected to the first winch and a second hawser connected to the second winch; a first sheave and a second sheave disposed on a second end of the tender opposite the first end of the tender, the first sheave for engaging the first hawser and the second sheave for engaging the second hawser; a first hawser fairlead disposed on a first side of the tender for receiving the first hawser and a second hawser fairlead disposed on the second side of the tender for receiving the second hawser and wherein said first hawser crosses said second hawser three times as each is reaved to each fairlead and wherein the first and second hawsers pass beneath the deck of the tender to the deep draft caisson vessel; at least one connector or joining the first and second hawsers at a position on the deep draft caisson vessel, after the hawsers pass each fairlead.